Computer printers each typically have a printing speed capacity designated in pages per minute (ppm). Some uses require very high speed printing, such as when many copies of a large document are needed in a short time. High speed or high volume printing is also needed in applications where substantial daily printing volume is required, even when no job is particularly urgent, such as in a large office with many users sharing a single printer.
High speed printers having printing rates above 100 ppm are available, but these are very expensive, even when considered in comparison to conventional printers on the basis of cost for a given daily capacity (i.e. the cost of ten printers each operating at one-tenth the speed of the high speed printer is much less than the cost of a single high speed printer.) In addition, high speed printers are typically limited to a single printing technology, typically black toner-based laser printing. Thus, for documents having some color, even a single color cover page, another printer must be used, or pages manually collated into documents from different printers after printing.
To provide high capacity, many offices with significant printing demands use a large number of low capacity printers, such as one for each employee. The printers may be networked so that one person may send a print job to any of the printers. This provides a high total capacity at a low cost, but lacks the capacity to conveniently print a large job quickly. A user needing many copies of a large document might ask each printer on the network to print a copy, but this is a cumbersome process requiring repeated print commands, and inconvenient collection of printed output scattered throughout a facility.
Cluster printing systems have been developed that use several printers controlled by a common controller that allocates printing jobs to the printers. On a job requiring multiple copies of a single large document, the controller may have each printer working on its own copy of the document, so that the output may be collected without sorting or collation. If a system were developed with different types of printers in the cluster, moderate speed laser printers may be used for printing monochrome documents such as conventional text, while a color printer may be used for documents containing any color printing. However, this system would not permit the use of more than one printer for different printing needs within a single document (such as for a color illustration page contained in an otherwise black text document), without introducing manual collation challenges.
When existing cluster systems are used by multiple users for different size print jobs, throughput may be optimized by scattering the load among the different printers, so that some documents may be printed on multiple printers, and some printers may be working on multiple documents. However, this creates a complex collation problem. Jobs and job portions may be identified by printing an initial identifying cover sheet that aids in the identification and reassembly of documents, and this cover sheet might be made machine-readable so that the process may be automated. However, the use of cover sheets consumes printer resources such as paper, ink, and throughput capacity.
The present invention overcomes the limitations of the prior art by providing a method of printing a plurality of documents including generating a page file for each page of each document, generating a control file for each page file, and operating a number of printers to generate printed pages based on the page files. The method includes scanning the printed pages to generate a scan file for each page, and identifying the corresponding control file to permit the printed pages to be segregated into properly sequenced separate documents.